#!/usr/bin/env python
# coding: utf-8

# In[1]:


a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]


# In[2]:


for row in a:
    print(row[0])


# In[3]:


for row in a:
    for element in row:
        print(element)


# In[4]:


for i in range(3):
    print(a[i][i])


# In[5]:


for i in range(3):
    print(f'The {i + 1}-th diagonal element is: {a[i][i]}')


# In[ ]: